Vacuum cleaner



July 14, 1953 Q. E. MEYERHOEFER VACUUM CLEANER 3 Sheets-Sheet 1 Filed March 24, 1949 INVENTOR. 1 far! E flag 0406f July 14, 1953 c. E. MEYERHOEFER VACUUM CLEANER 3 Sheet-Sheet 3 Filed March 24, 1949 INVENTOR. garl, E Magerfiae/er Patented July 14, 1953 UNITED Y STATES v PATENT OFFICE Carl E. Meyerl i ii fl l ri lfl yfil il, assignor to Lewyt Corporation, Brooklyn,

tion of New York N. Y., a corpora- Application March 24, 1949, Serial No. 83,147

This invention relates to a structurally and functionally improved vacuum cleaner.

8 Claims. (Cl. 18359).

It is an object of the invention to furnish a unit of this character which will embody an improved design and by means of which the mechanism may operate over prolonged periods of time without it being necessary to empty the dust receiving compartment of the same.

A further object'is that of furnishing a device of this character which will include relatively few parts each individually simple and rugged in design, such parts being capable of ready assemblage to furnish a mechanism operating over long periods of time with freedom from all diffieulties.

With these and other objects in mind, reference is had to the attached sheets of drawings illustrating practical embodiments of the invention and in which:

Fig. l is a sectional side view of a preferred form of vacuum cleaner;

Fig. 2 is a sectional plan viewof the filter'supporting assembly as shown in Fig. 1;

Fig. 3 is a side elevation of thatassembly with certain of the parts broken away to show underlying structures and also with certain of the parts being shown in section;

Fig. 4 is a side elevation of an alternative form of cleaner structure with certainof the parts broken away to disclose underlying mechanisms;

Fig. 5 is a fragmentary enlarged sectional view of certain of the parts as shown in Fig. 4;

Fig. 6 is a transverse sectional view taken along the lines 6-6 and in the direction of 'the arrows as indicated in Fig. 5;

Fig. '7 is a view similar to Fig. 4, but showing alternative lay-out of the mechanism and design of cleaner;

Fig. 8 is a side elevation of a cleaner similar to that shown in Fig. 1 but embodying an alternative form of construction and with certain of the parts broken away to disclose the interior mechamsm;

Fig. 9 is a fragmentary detail of the upper portion of a filter unit showing an alternative structure; and

Fig. 9-A'is a similar view of the lower portion of such structure.

Primarily referring to Figs. 1, 2 and 3, it will be seen that the reference numeral It indicates a casing which may have a cylindrical outline and be provided with a cover assembly. The latter rests upon a gasket ll upon which there may be disposed a filter element I2. The latter as illustrated is a cone and is formed of airner and upper surface of gasket H .a diameter substantially equal to that surface.

2 pervious material such as collar 13 may extend from the exterior face of the casing ID and be disposed in line with an opening [4 formed through the wall of that casing. A deflector member or elbow I5 may beattached to the inner face of the casing and extend in a manner such that incoming air is diverted in a path generally parallel to theinner face of the casing. The collar 13 provides a con venient coupling or mounting for the inner end of a hose or other suitable unit (not shown) such as is customarily connected to a vacuum cleaner. 7 i

The cover assembly mounts the motor and fan unit and includes a number of parts. As shown, it conveniently embraces an outwardly extending portion l5 providing a flange. The latterwhen the -parts are assembled-overlies the gasket H as well as the downwardly extending edge portion ll of the filter element [2. A downwardly and inwardly extending ring portion 48 may be coupled to flange 16. This ring extends in a direction substantially parallel with the inand has Therefore, when the cover assembly is in position'upon the casing, it is apparent that a substantially air-tight seal will be furnished between the adjacent surfaces of ring l8 and gasket H.

Also, the interposed material of filter element t2 will befirmly gripped to prevent a displacement of the latter. It will be appreciated that while not shown, catches or securing elements are furnished which extend between the casing l0 and cover assembly to prevent an accidental displacement of these parts with respect to. each other and to additionally maintain the aforementioned seal and gripping functions.

The ring l8 may mount a flanged member I9 supporting the upper edge of a second filter element 20 conveniently formed of cloth. As shown, the surfaces of elements l2 and 20 mayunder the initial positioning of the partsextend in parallel and'spaced relationship. Flange It may becontinued upwardly as at 2| and is interrupted by ports 22 above which a casin portion 23 ex tends upwardly and inwardly. A detachable cover 24 maybe provided with a handle 25 and mount an inwardly extending deflecting cone 2B. This may be supportedupon pin 21 secured to inwardly and downwardly extending continuations 28 of the casing portion 23. These continuations preferably define a central chamber which is normally completely sealedby the cover 24. As illus- 3 trated, the continuation may be formed with a.

a suitable paper.

may be disposed adjacent the upper ends of the ducts 22., The space intervening this plate and the perforated member 29 may be filled with a sound-deadening material. Within the ducts 22 deflectors 32 may be disposed so as to divert air fiowingfthrough the ducts in an outward direction.

Supported as part of thecover assembly is .a. motor 33, the shaft of which operates a fan 34.

The latter as illustrated may be a multi-stage assembly and is enclosed in a casing 35 having a lower opening for the entrance of air. An electric cable 36 extends through an opening in the coverv assembly and is connected to a switch 37 which may be operated by a pivotly mounted pedal 38 extending beyond the cover and preferably in line with the zone of the ducts. This switch is of a the type in which one projection and release of its.

actuator 39 serves to close the circuit through its parts. A second projection of the actuator serves to open such circuit. The pedal 38 may present a thickened portion 48 in line with the actuator 39 to provide a suitable bearing surface at a point beyond the pivot 4| of the pedal. I

Thus, as taught in the United States Letters Patent in name of Carl E. Meyerhoefer and Alex M. Lewyt on Vacuum Cleaner, No. 2,516,707, dated July 25, 1950, anoperation of the parts will occur as follows: i

Dust-laden air will enter the opening I4 and will be deflected into a circular path by the -baille [5. Heavy particles of dirt will be thrown against the wall of casing IE] by centrifugal force and drop to the bottom of that casing. The dust and other foreign material remaining in suspension in the air. will be prevented from continuing to move with the air stream incident to the filtering action exerted by element l2. It will be understood that the layer of cloth or other material acts as a secondary filter to remove from the air any remaining dust particles which may have passed through filter element l2 incident to a rupturing of the latter or otherwise. Also, it will be understood that filter element 20 will function as an emergency filter in the event that no element [2 has been positioned within the casing. In any event, the air will pass upwardly through the opening in the lower face of casing and thence through the fan assembly 34. It will continue to flow upwardly beyond the latter and with the cover 24 in position, will be deflected by unit 26 through the openings or perforations 29. Thence it will flow downwardly and outwardly and pass through the perforations or openings of plate 3| and so outwardly through the ducts or ports through which it is guided by the deflector 32. The material interposed between the perforated plates 28 and 3! will serve as a further filter in addition to functioning to suppress unnecessary noise. The entire unit may be transported by handle 25. The latter may also be manipulated to effecta detachment of cover 24 from the cover assembly. When so detached, a hose or similar accessory may be coupled to th discharge collar 42 so that the apparatus may function as a blower for spraying, de-mothing, or other purposes.

Contrary to the construction illustrated in the afore-mentioned prior application for patent, the straps 43 which preferably extend downwardly by a spring 48.

- '4 from the casing 35 and the supporting structure adjacent the same, slidably mount a vertically disposed pin or rod 44. As especially shown in Figs;

2 and 3, these straps may intersect at a angle and at zone of intersection may be secured together by welding or in any other suitabl man- 'ner. Within their zone of intersection, they are formed with aligned openings through which a common eyelet 45 may extend to furnish a suitable guide for rod 44. One of these straps may also have to secure to it, by spot welding or otherwise,

an inwardly extendin supplemental strap 46.

' The latter is formed with an opening in line with the eyelet 45 and thus slidably mounts the in- .ner endof rod 44., A nose piece or support 41 is secured to the outer end of rod 44 and the latter is urged in anoutward or downward direction Such spring may be interposed between the nose piece 41 and the surface of the lowermost strap 43. The upper or inner end of rod 44 may .be formed with a groove which receives a restraining member conveniently in the form of a spring washer ,9. Thus, the spring is prevented from shifting th rod outwardly beyond predetermined limits... 7

With a view to providing a structure which will retain the rod in retracted position, the latter may be formed with a keeper groove 50. A bolt in the form of a latch plate 5| may haveone of it ends pivotly coupled as at 52 to one of the strap members 43 and to one side of the center zone of the latter. A guide 53 may extend from the upper surface of this strap to the other side of its central zone and cooperate with the latch plate to prevent a flexing of the latter. A spring 54 has one of its ends secured to the second strap 43, its opposite end beingcoupled to the latch plate 5!. As shown, the latter may be formed with an opening 55 to one side of its'point of Thelower end of the wire may be secured to the latch byextending through the opening 55 of the latter. That opening being relatively closely spaced from the pivot 52, it follows that a com-. paratively small shifting of the wire 58 will result in an appreciable swinging of the latch plate 5|. While the wire will be maintained in a taut condition, it will normally occupy a position such that the latch will be in operative relationship to the rod 44. This may be assured by associating a spring 60 in cooperation with the pivot 41 and treadle 38. Thus, the outer end of the latter will tend to occupy a raised position.

It will be understood that in the operation of the cleaning mechanism, particle of dust willas afore brought outimpinge against and adher to the outer surface of filter element [2. As this coating of dust or other dirt increases in thickness, a layer which is substantially impervious to the passage of air will be built up. With such a layer in existence and increasing in thickness, the efiiciency of the apparatus decreases ar replaced It will be additionally understood motor may be formed that .with; theyfan. assembly operating, a @consid-i erable differential. in pressures will exist between. the spaces exteriorly of the filter eler'nentorele-v mentsrand the space interiorly. theretoi. .With the rod 44 resiliently supported, it is' apparent. that the. filter elements functioning asdiaphragms in response to this differential, will. cause the rod to' be. retracted against theaction. of :itsspring. This retraction will continue (as thelayer of dust.

builds up) until the, keeper. groove 5011s in, line with the latch plate 5|. Under; the influence of.

spring 54 the edge of this: plate will enter the keeper groove. Accordingly, the rod'will. be prevented from further shifting. Anystrain which would. be imparted to pivot 52. incident t'oarod (M.

attempting to further retract, will be relievedwby guide 53. Under these circumstancesthe parts of the cleaner will function. as. heretofore.de-

scribed.

The layer of dust and other dirt will continue.

to build up on the outer surface of. the filter element and upon completion of the cleaning operation, treadle 38 or it equivalent may be operated to cause a functioning of theactuator 39 and an opening of. the mechanism of the switch 31. This will cause a discontinuance of operation of the motor 33. i

Despite the fact that coincident with operation of the treadle the cable 581wil1 be retracted, this will not result in, a projection of rod 44; rather the rod will remain retracted because. several seconds will elapse before the fan comes to a stop.

During the major part of this interval, due to the momentum of the fan and the flow. ofair, the filters. will continue to react to such pressure differential as continues to exist. Therefore the operator will have released the treaidle and'thus maintain the latch in position within the keeper groove before the spring returns rod 44 to its initial position.

However, if th parts are once allowed to come to a position of rest, then the apparatus is potentialized in a manner such that excess dirt will be removed from the face of the filter element when the parts are next operated. Thus, with the motor stationary, but with the operator ready innerface of filter layer 20,this layer as well as.

layer [2 will be snapped to a condition of tension. Dust and dirt particles have the tendency of building up into a somewhat homogenous 1ayer. With such snapping action that layer will be expelled from adhering contact withthe surface of the filter and will fall as arelatively weighty skin (either in large or small units) to the base of the casing 10. Thus, the efficiency of the filter will be re-established. It will be understood that this freeing of the filter will occur despite initiation of the motor operation because the snapping action will occur even before the switch is closed. It will take an appreciable interval of time thereafter for the motor and the fan assembly to come up to speed and to re establish a differential pressure'action such that the layer would tend to remain adhered to the outer face of the filter element. Of course, the

operator will not be consciousin the structure of Figs. 1 to 3 that any latch releasing function has occurred. Rather, that operator will only visualize that the switch has been closed incident to moving the treadle 38 downwardly.

The same functional results may be achieved in a cleanerof the type shown in Figs. 4, 5,

and 6. In these views, the numeral 6| indicates.

a casing within which a bag-typefiltering element 62 may be mounted in any approved manner. Conveniently the base of this filtering element (with which a paper filter may be associated if desired) mounts a plate 63. The latter is formed with perforations through which air may flow and a clamping ring 64 may be retained in association with the plate by means of a This threaded stem and wing nut assembly 65. stem forms a part of a slidably mounted rod 66 which may be supported as at B1. A keeper groove '68 is formed in this rod and a bell crank lever 69 may be pivotly mounted adjacent the same and have one of its arms providing a latch portion cooperating therewith. A spring 1!! normally holds the filtering element or bag 52 in a.

position to the left of that shown in Fig. 5.

A spring 1! cooperates with the latch lever 69 so that the latter tends to enter the keeper groove 58. The operating treadle or actuator 12 disposed on the exterior of the casing and which serves to cause a functioning of switch I5, also cooperates with a slidably mounted rod 14. The latter extends to a point at which it contacts the second arm of lever 69. With a view to imparting a twisting motion to the filter such that particlesadheringito the face of the same will be subjected to a maximum freeing action, rod 56 may be formed with a spiral groove 15. A dog or pin 16 carried by the guide 61 may ride within this slot.

As is apparent with the initiation of motor and fan operation in accordance with conventional structures of this type, a differential pressure. action will be set up. This will cause bag 82 to be expanded so that plate 63 will move to the rightas viewed in Figs. 4 and 5. This will serve to compress spring 10 and with such compression the latch will function to maintain the parts in retracted position. The operation of the cleaner. may now be continued until it is desired to have the motor cease operation. At that time an op I structure engaged. A subsequent operationof actuator 12 will release the latch. Thus, under the action of spring l6, rod 66 will berapidly projected and thereupon have'its motion arrested by the stop 11. Due to the momentum of the parts, any layer of dust and dirt will be snapped from the surface of the filter. This will be es pecially true if the spiral groove is is employed to assure a rotation of the parts in addition to an axial movement of the same. I

As is apparent, the structure shown in Figsl 4, 5 and 6 may be adapted to a vacuum cleaner of f the type shown in Fig. '7 in which the numeral '18 indicates a casing containing a motor T9 and fan assembly. In this form of structure, the inlet 7 communicates with a filter 81 similar to filter 62, b ut which is conveniently above areceptacle 82. Again a plate 83 and spring-pressed rodM- to operate.

surface.

are present, as are also. the switch treadle 85, a rod corresponding to the rod 14, a latch etc.,

7 as heretofore described in Figsxl to 6.

When the motor 19 is operated, then the filter 8!, due to the differential in pressure, will be expanded and cause a retraction of rod 84 which will be latched in position. Thus, the parts'are potentialized for removing an adhering layer of dirt. The parts will continue in this position and will remain even after the motor-TF9 has ceased In a subsequent operation a movement of the treadle 85 will release the latch. Thus, the adhering particles or layer will be snapped from the filter BI and its associated parts will drop into the receptacle 82. The latter as shown, being out of the path of the air flow, will retain these particles. It may be periodically emptied but the filter element will not require cleaning.

While in many respects it is preferred'that the cleaning of the filter surface occur without any conscious action on the part of the operator, this need not necessarily be the case. .The present invention contemplates a deliberate operator manipulationto achieve the desired result. Thus, as in Fig. 8, the treadle 86 may serve to close and open switch 8i to cause operation and cessation of operation of the motor-driven fan assembly precisely in the manner as heretofore-described in Figs. 1, 2 and 3. being substantially identical with the parts described in these earlier figures, the same reference numerals have been generally employed. However, in Fig. 8, the wire 83 which efiects a retraction of the latch may be secured to a separate treadle 89 pivotally mounted at at fit.

Therefore, the operator may use a vacuum cleaner, and in such use, the layer of dirt may build up on the surface of the filter element or elements. In such operation, the latch will become operative due to the differential in pressure and the apparatus will be potentialized so that the layer of particles may be snapped from its surface.

When the motor has ceased functioning, then an operation of treadle 89 will cause a pull to be exerted on wire 88. This will release the latch and the layer will be snapped free incident to the movement of the spring-pressed rod or plunger. Thereupon, treadle 86 may be operated to again initiate an operation of the motor and fan. As

' will be understood in connection with the forms described and illustrated under Figs. 1 to 3 and 8, the filter assembly is maintained in what might be termed a condition of slack with the unit operating. This will be true whether that assembly includes a single filtering layer, two layers, or a more complex structure. With respect to the forms shown in Figs. 4 to '7 inclusive, the filter assembly under operating conditions is maintained in a relatively tautened state. However in those forms the major surface of the assembly to which dirt adheres will be the inner Regardless of this, however, when the filter is once in potentialized position its release in all forms will cause the adhering cake of dirt to be snapped from the filter surface so that air may again freely pass through the same. In addition to this snapping action it will, of course, be appreciated that the flexing of the filter assembly in all forms would tend to initiate a cracking of the cake surface so that the latter will tend to drop from an adhesive contact with the filter even without the aforementioned snapping action. If that actionis accompanied by a twist- The partsaction of spring 48.

ing action as in Fig. 5, the loosening of the particles will occur in an even more positive manner than otherwise.

The structure need not necessarily involve a movement of one part of the filter assembly with another portion of the same retained against movement. Rather, as in Figs. 9 and 9A the entire filter assembly may be movable. Thus, in these views it will be observed that 9| indicates a supporting portion similar to the part 18 in Fig. 1. The numeral 92 indicates a clamping ring which mayretain the edge of a boot 93 in'position. This boot may be of rubber. The lower edge of this element may be enlarged as at 94 and serve to mount clamping hoops 95 which thus removably retain a filter assembly. That assembly may embrace an inner part 96 and an outer parts 91. Each or both of these parts may include any suitable number of layers formed of cellulose sheeting or any other desired material. One of the layers should comprise a relatively coarse screen for stiffness. The outer layer may embrace, for example, a 325 mesh screen arresting the passage of particles larger than microns in any direction. The inner cellulose sheeting will stop particles-smaller than 45 microns in any direction.

It will be appreciated that the mechanisms in thesetwo latter figures will operate practically identically with the operation of the mechanism in Figures 1, 2, and 3. However, instead of the upper edge of the filter assembly being retained against movement and the lower part of the assembly shifting the entire assembly will move as a unit. More particularly, as operation is initiated rod Mv will be pressed back against the The assembly 96-9! will shift from the position shown in full lines in Fig. 9 to that indicated in dash and dot lines in that figure. This will be because of the flexibility or resiliency of boot 93. When the latch is released and after the parts have ceased functioning, rod 44 will be projected and the entire filter assembly will be snapped in a manner such that particles of dirt adhering thereto Wil1 be forced out of adhering contact with the surface of the filter. complished.

Thus, among others, the several objects of the invention as specifically aforenoted are achieved. Obviously numerous changes in construction and rearrangement of the parts might be resorted to Thus, the desired results are acwithout departing from the spirit of the invention as defined by the claims.

I claim: 1. In a vacuum cleaner in which in response to a closing of a motor controlling switch-ac tuator a suddenly arrested motion is imparted to the filter of the cleaner prior to the initiation of substantial air flow through the latter so that particles of foreign matter are impelled away from the surface of such filter, said cleaner comprising .a casing formed with inlet and outlet openings, a motor-driven fan within said casing for causing a flow of air from the inlet to the outlet opening, a filter through which said air flows, supporting means retractable in response to the establishment of a condition of air pressure as provided by the operation of said fan, means for retaining said supporting means in retracted position upon the cessation of fan operation, a switch-actuator for controlling the motor of said fan and means connecting said actuator with said retaining means to release the supporting means for projection and impart a suddenly arrested motion "to said aaaaa that to a closing of'a motor controlling switch-ec- 10 or the same against movementwith respect to said casing and with movable portions of said filter extending across said casing and intersecting the path ofdust-ladenair' entering said inlet opening and passing towards said outlet opening; motor driven means supported by said casing to cause such air'fiow, a retractable suptuator asuddenly arrested motioni'simpartedto I the filter of the cleaner prior to thefiriitiatioii of substantial air fiow throughthe'latterso 'that particles of foreign matter are impelled away from the surface of such filter, said cleaner comprising a casing formed with inlet and outlet openings, a motor-driven fan within said casing for causing a flow of air from the inlet to the outlet opening, a filter through which said air flows, a spring pressed filter supporting means, means for mounting said supporting means to be retracted in response to pressure asserted by the filter when a condition of air pressure as provided by the operation of said fan exists, means for retaining said supporting means in retracted position upon the cessation of fan operation, a switch-actuator for controlling the motor of said fan and means connecting said actuator with said retaining means to release the supporting means for projection and impart a suddenly arrested motion to said filter, suchthat particles of foreign matter are impelled away from said filter 'prior to the establishment of a substantial air fiow through the body of the latter.

3. In a vacuum cleaner in which in response to a closing of a motor controlling switch-actuator a suddenly arrested motion is imparted to the filter of the cleaner prior to the initiation of substantial air fiow through the latter so that particles of foreign matter are impelled away from the surface of such filter, said cleaner comprising a casing formed with inlet and outlet openings, a motor-driven fan within said casing for causing a flow of air from the inlet to the outlet opening, a filter through which said air flows, a spring pressed filter supporting means, means for mounting said supporting means to be retracted in response to pressure asserted by the filter when a condition of air pressure as provided by the operation of said fan exists, a latch cooperating with said supporting means to retain the latter in retracted position upon the cessation of fan operation, a switch-actuator for controlling the motor of said fan, means for connecting said actuator with said latch means to release the supporting means for projection by its spring and a stop for suddenly arresting the motion of said filter in a, manner such that particles of foreign matter are impelled away from said filter prior to the establishment of a substantial air flow through the body of the latter.

4. In a vacuum cleaner a casing formed with inlet and outlet openings, a motor-driven fan assembly within said casing for providing an air flow therethrough, a slideably mounted spring pressed support extending below said fan and to engage a filter and be retracted thereby upon the establishment of pre-determined conditions of air pressure within said casing by said fan, a latch cooperative with said support to maintain it in retracted position, a movable actuating member extending beyond said casing and means connecting said member with said-latch to release the latter.

5. A vacuum cleaner including in combination a casing formed with inlet and outlet openings, a support for a flexible filter to secure portions 'portdispo'sed between said filter and said outlet opening, means :for yieldingly resisting retractiveimoveinentof said support, the air flow through said casing causing a differential of pressureupon' opposite sides of saidfilter which differential. increases as the filter material becomes dust-clogged, said increase in pressure differential causing movement of the'fi'lter portions and pressure thereof against said support such that thelatter is retracted, latch means for retaining said ssupport in retracted position; a

switch actuator for controlling the operation of said motor-driven: means and means connected to said'actuator andlatch means for releasing the latter substantially simultaneously with the operation of said, switch whereby said support will be'projected, by said yielding means to tension said filter and impel dust from its surface.

6. A vacuum -cleaner:including in combination a casing formed, with inlet and outlet openings, a support for a flexible filter to secure portions of the same against movement with respect to said casing and with movable portionsof said filter extending acrosssaid casing and intersecting the path of dust-laden air entering said inlet opening and passing towards said outlet opening, motor-driven means supported by said 1 casing to cause such air flow, a retractable support disposed between said filter and said outlet opening, means for yieldingly resisting retractive movement of said support, the air fiow through said casing causing a differential of switch and'actuator assembly, said switch functioning in response to successive operations of said actuator to energize and de-energize the motor-driven means and means controlled by said actuator and functioning substantially simultaneously with the closing of said switch to release said latch means whereby said support will be projected by said yielding means to tension said filter and impel dust from its surface prior to the time when the motor-driven means reaches its maximum speed.

'7. A vacuum cleaner including in combination a casing formed with inlet and outlet openings, a motor-driven blower mounted by said casing to cause a fiow of air from the former through the latter opening, a filter support movable within said casing and normally occupying a position such that the filter engaged thereby is maintained in a taut condition, a latch assembly comprising a keeper portion associated with said support and a bolt, means for movably mounting said bolt within said casing in a position such that it engages said keeper and maintains said support in a retracted position to which it has moved in response to increasing pressure exerted by air in its passage through the material of the filter and as dust particles clog the material. of the same, a switch actuator movably mounted by said casing, a switch operated by said actuator and con- 11 nected to the motor of said blower to initiate and interrupt the operation of the latter in response to, successive movements of said actuator and meansconnecting the bolt for retraction by said a motor-driven blower mounted by said casing to cause a flow of air from the former through the latter opening, a filter support'movable within said casing and normally occupying a position such that the filter engaged thereby is maintained inia tautened condition, a latch assembly comprisinga keeper portion associated with said'support and a bolt, means for movably mounting saidv bolt within said casing in a 'position such that it engages said keeperiand-maintains said support in a retracted position to which it has moved in response to increasing pressure exerted by-air in its passage through the material of the filter and as dust particles clog the material of the same, a switch actuator movably mounted by said casing, a switch operated by said actuator and connected to the motor of said blower to r 12 initiate and interrupt theoperation of the latter in response to successive movements ofsaid actuator, means connecting the bolt for retraction by said actuator as the latter is moved whereby with the keeper portion engaged by said boltsaid support'will be released for projectionto tauten said filter substantially simultaneously with the initiation. of motor operation and a spring, connected to the filter support for urging it into said normal position.

" CARL E. MEYERHOEFER.

References Cited in the file of this atent V V UNITED STATES PATENTS Number Name 7 Date 1,933,105 Forsbergj l; Oct. 31, 1933 1,991,859 Lofgren Feb. 10, 1935 2,192,224 Forsberg Mar. 5, 1940 2,242,277 Yonkers May 20, 1941 2,443,162 Hallock June 8,1948 2,541,122 Sparklin Feb. 13, 1951 2,564,468 Anderson Aug. 14, 1951 FOREIGN PATENTS Number Country ,'Date 63,725 Denmark July 9, 1945 Netherlands 'Jan. 16, 1946 

